The field of the disclosure relates generally to breast imaging systems, and, more particularly, to breast imaging systems including ultrasound and x-ray using a dual-sided compression paddle system and the methods of operation for acquiring breast images.
Breast cancer screening is performed with x-ray imaging in either two-dimensional, i.e., mammography, and in recent years, tomosynthesis (three-dimensional x-ray). For many women, such x-ray screening is sufficient for generating images that are satisfactory for review by a medical professional. However, many women have a high percentage of dense breast tissues which do not show contrast versus cancerous tissues and additional screening is performed through ultrasound imaging. Ultrasound imaging is often performed in a supine position whereas the x-ray mammography is performed with the women upright with the breast in a compressed position. Such shifting of position of the patient shifts the shape and the tissue of the breast making any registration of the two imaging modalities difficult. As a result, significant discrepancies between the findings in the mammography and the ultrasound images may require further imaging to resolve and my lead to unnecessary biopsies. Therefore, it is highly desirable to perform the mammography or tomosynthesis imaging in the exact same positioning at the same time as the ultrasound imaging. To perform ultrasound imaging, the ultrasound probe must be in contact with the tissue or a coupling medium such as ultrasound gel or lotion or water. However, if the ultrasound gel is applied to the breast prior to taking the x-ray image it may result in artifacts in the x-ray image.
In addition, in order to achieve high x-ray image quality, either mammography or tomosynthesis, one must have as small of a distance between the x-ray detector and the breast as possible. Therefore, to preserve optimal image quality between x-ray imaging and ultrasound imaging one must move the ultrasound transducer and coupling medium between the x-ray source and/or detector and the breast.
Previous attempts to design breast screening systems that integrate both x-ray and ultrasound technologies have had not completely addressed the workflow and image quality needed in both the mammography and ultrasound. In previous examples, the woman's breast is compressed as for standard mammography imaging and the x-ray image acquired. Upon completion of the x-ray image the breast is scanned with the ultrasound probe on top of the compression paddle on the breast. This configuration gives very good mammography image quality. However, the ultrasound image quality is degraded as resolution is limited by the frequency of the ultrasound due to an inverse relationship between the frequency of the ultrasound signals and the penetration depth of the sound waves, i.e., the sound attenuation is proportional to the frequency and higher frequency ultrasound may not adequately penetrate the breast tissue. In most breast-compressed thicknesses the ultrasound frequency needed to fully penetrate the breast does not give sufficient imaging resolution to detect small masses and calcifications.
In other systems, where the breast is scanned from below, the ultrasound attenuation issue described above remains and additionally coupling medium for the ultrasound probe absorbs a significant portion of the x-rays after exposing the patient. This results in necessitating a higher x-ray dose to the patient. Furthermore the distance between the x-ray detector and the patient is increased. This may result in degradation of the x-ray image quality as well.
Dual sided scanning with ultrasound on a separate system in the mammography configuration has also been demonstrated. In this configuration the ultrasound image quality has been preserved. However, the workflow and image registration have proven difficult, since movement of the breast being imaged is likely. It is highly desirable to incorporate the high image quality of dual sided ultrasound scanning in the mammography configuration without requiring the use of a separate system. In order to perform dual sided ultrasound scanning of the breast on a mammography system, one solution is to include features that move the x-ray detector out of the way such that the ultrasound probe can be moved into position once x-ray imaging has been performed. However, for many known x-ray systems the detector is attached x-ray system gantry and does not move. For these systems an ultrasound only add-on is highly desirable.